1. Field of the Invention
The present invention relates to a spin-valve giant magnetoresistive head for reproducing magnetic information written in a minute single domain on a magnetic recording medium in a magnetic recording apparatus for use in a computer, an information processing apparatus and the like. In particular, the present invention relates to a spin-valve giant magnetoresistive head and its manufacturing method suitably used to prevent instability of magnetoresistive (MR) output voltage waveform caused by Barkhausen noise and obtain adequate MR output voltage, especially in a narrow-track head necessary to achieve high-density magnetic recording.
2. Description of the Related Art
A thin-film magnetic head for writing and reading magnetic information is a key device to a magnetic recording apparatus. The thin-film magnetic head consists of a inductive write head for writing magnetic information and a read head for reading out the magnetic information written in a recording medium.
The read head for reading out the magnetic information from the recording medium includes a magnetoresistive element showing a resistance change to a very weak magnetic field applied from the outside, or a giant magnetoresistive element showing a resistance change larger than that of the magnetoresistive element. The reproducing head also includes a conductive film for supplying sensing current for use in sensing the resistance change.
The spin-valve giant magnetoresistive head that shows a large MR ratio to an applied magnetic field to produce a resistance change to a very weak magnetic field includes multiple thin films of giant magnetoresistive (GMR) sensor. The multiple thin films of GMR sensor are composed of at least an antiferromagnetic layer, a pinned magnetic layer, a free magnetic layer, a nonmagnetic conductive spacer that achieves magnetic insulation between the pinned magnetic layer and the free magnetic layer, and a nonmagnetic protective layer. The spin-valve giant magnetoresistive head also includes magnetic-domain control layers that maintain the magnetic orientation of the free magnetic layer in such a state that it intersects at right angles to that of the pinned magnetic layer. Further, the spin-valve giant magnetoresistive includes a conductive layer that supplies sensing current to the multiple thin films of GMR sensor to sense the resistance change.
In the spin-valve giant magnetoresistive head, a magnetic field necessary for magnetic-domain control is applied to the free magnetic layer to make a single domain of the free magnetic. This technique is important for preventing instability of MR output voltage waveform caused by Barkhausen noise.
FIG. 11 shows an exemplary cross-sectional structure of a conventional spin-valve giant magnetoresistive head as seen from the side opposite to magnetic recording media. First, a lower magnetic shield layer 41 is formed, and a lower insulated gap layer 42 is formed on the lower magnetic shield layer 41. Then, on the lower insulated gap layer 42, multiple thin films of GMR sensor D2 are formed in a trapezoidal cross-sectional shape. The multiple thin films of GMR sensor D2 are composed of an antiferromagnetic layer 1, a pinned magnetic layer 2 formed on the border of the antiferromagnetic layer so that its magnetic orientation can be aligned in a fixed direction, a free magnetic layer 4, a nonmagnetic conductive spacer 3 that achieves magnetic insulation between the pinned magnetic layer 2 and the free magnetic layer 4, and a nonmagnetic protective layer 5.
Magnetic-domain control layers 9 are formed on the side inclined parts of the multiple thin films of GMR sensor D2 and the lower insulated gap layer 42. The magnetic-domain control layers 9 make the magnetic orientation of the free magnetic layer 4 aligned in such a direction that it intersects at right angles to the magnetic orientation of the pinned magnetic layer 2. Base material layers 8 for the respective magnetic-domain control layers 9 are formed under the magnetic-domain control layers 9. Conductive layers 11 for supplying sensing current to the multiple thin films of GMR sensor to sense a magnetic resistance change are formed above the magnetic-domain control layers 9 through base material layers 10 for the respective conductive layers 11. An upper insulated gap layer 47 and an upper magnetic shield layer 48 are formed over the multiple thin films of GMR sensor D2 and the conductive layers 11.
In such a spin-valve giant magnetoresistive head, a magnetic field enough for magnetic-domain control is applied to the free magnetic layer 4, which makes it possible to prevent generation of Barkhausen noise, and hence instability of MR output voltage waveform. Thus a stable head can be provided.
One approach to reducing Barkhausen noise to prevent instability of MR output voltage waveform is described, for example, in JP-A-2000-215424. This publication presents such a structure that a flat part of a hard-bias layer having larger thickness than that of a free magnetic layer is positioned in the thickness direction of the free magnetic layer at the same level as the free magnetic layer. The free magnetic layer corresponds to the above-mentioned free magnetic layer 4. The generation of instable MR output, however, cannot be prevented by this approach alone.